With the widespread use of Internet and advances of the multimedia and communication technologies, various digital contents are distributed and acquired over the network. However, without copyright protection policy, the advanced network environment and technologies are likely to be used for illegal distributions of the contents.
Digital Rights Management (DRM) systems have been developed to prevent the illegal use and distribution of the copyrighted contents. DRM is a term that refers to access control technologies for protecting the copyrights of the authors and the content providers.
The DRM is specified to provide a controlled consumption of digital contents and to protect the intellectual property right of the authors and the content providers.
Typically, encrypted DRM contents can be freely accessed and downloaded. In order to use the DRM contents, however, a license called Rights Object (RO) is required for decoding the encrypted DRM contents. With its efficient usage control, DRM is used by many copyright holders.
DRM technologies attempt to protect the digital contents through all the phases of creation, distribution, use, and abrogation; and restricts access and usage rights of the user on the digital contents. DRM allows the user having a valid encryption key such as RO to decode the encrypted digital content such that the digital content can be protected even when being illegally distributed.
The RO is a container used in the OMA DRM system, which is an open DRM standard invented by the Open Mobile Alliance (OMA), for carrying the license key to decrypt the corresponding DRM contents. The RO is issued by a Right Issuer (RI) and purchased by the end user. Since the digital content and corresponding RO are delivered in a detached manner, the usage of the downloaded content is restricted to the user who acquired the corresponding RO.
The RO is a collection of Permission, Constraints, and other attributes that define under what circumstances access is granted to, and what usages are defined for, DRM content object. Typically, the usage constraints include Count, DateTime, Interval, Timed-Count, Accumulated, and Individual. The constraints are stored in a specific field of the RO.
For example, the RO may specify the usage for an MP3 file with the count constraint value set to “10”. In this case, the MP3 file can be played 10 times and the count is decremented by 1 whenever the MP3 file is played. If the count value becomes “0”, the usage right on the MP3 file expires. In order to maintain the usage right on the MP3 file, the corresponding RO should be updated.
FIG. 1 is a diagram illustrating RO delivery procedure in a conventional DRM system.
In FIG. 1, a mobile terminal 101 transmits a content request message (105) to content server 102, and the content server 102 transmits a corresponding content 106 in response to the content request message 105. In a case that the requested content is a DRM protected content, the content is encrypted with an encryption key and scheme specified by the DRM and transmitted in a DRM format having the constraints (e.g., usage rule, the number of times to be played, and duration). If a user request for acquiring the license to the downloaded content is detected, the mobile terminal 101 transmits a license request message 107 to a Right Issuer (RI) 103, and the RI 103 transmits the corresponding license 108 to the mobile terminal 101 in response to the license request message. Here, the license is a usage right on the content which includes a decryption key and usage constraint information. In the case of DRM content object, the mobile terminal 101 should acquire the usage right for consuming the content. Accordingly, the RI 103 checks whether the identity of the user of the mobile terminal 101 is valid. If it is determined that the user is valid, the RI 103 transmits the license to the mobile terminal 101. If the license is received from the RI 103, the mobile terminal 101 can play the content using the license. Typically, the decryption key and usage constraint information is extracted from the license by a DRM client application installed in the mobile terminal 101. The content is decrypted by using the decryption key and played under the usage constraints specified in the license.
However, the conventional DRM system has a drawback in that the RO acquisition or update process is performed item by item such that it is time consuming and cumbersome to acquire or update multiple ROs. That is, since the ROs required for consuming DRM content objects are purchased one by one, the user should perform the purchasing process repeatedly as many as the number of the DRM content objects, resulting in user inconvenience.
For example, when it is decided to update the expired usage rights on a MP3 file, a video file, and a game file, the user should purchase the ROs of the MP3, video, and game files one by one through respective purchase transactions. These repeated RO purchase transactions are time-consuming and cumbersome, resulting in contents management inefficiency and user inconvenience.